1. Field of the Invention
This invention relates to a bottom structure of a DC electric arc furnace.
2. Description of the Prior Art
A bottom structure for a DC electric arc furnace is constructed as follows. Refractories are laid on a steel base plate having sufficient mechanical strength. On the base plate is provided a connector for the connection of a power supply. Many thin electrode pins are mounted through the refractories and all the lower ends of the electrode pins are secured in the base plate. The thin electrode pins are used in order that the upper end portions of the pins may be less eroded by a molten metal pool in the furnace when the DC electric arc furnace is operated. Furthermore, a lot of electrode pins are used so that a sufficient electric current may be supplied to the molten metal pool in the furnace through the respective thin electrode pins.
When the DC electric arc furnace is operated, the electric current supplied by the power source flows to the many electrode pins from the above mentioned connector through the base plate and further to the molten metal pool in the furnace through the electrode pins. The furnace bottom structure of this type is disclosed, for example, in Japanese published unexamined patent applications No. 1-128392 and No. 2-287090.
The electric resistance of the above mentioned base plate, however, is relatively large since it is made of steel. Consequently, there appears a problem that a large electric current, which is to be supplied via the many electrode pins, does not flow so much through the electrode pins away from the connector but much of the electric current flows concentrically through the electrode pins close to the connector. Thus there is a problem that the concentration of electric current on some particular electrode pins increases the heat in the conductors carrying much of the electric current and may be a cause of bringing about an accident to melt the electrode pins. In order to prevent the concentration of electric current, it is considered to make the above mentioned base plate of copper. The base plate, however, reaches a high temperature when the furnace is operated. Then enough mechanical strength is not obtained with the copper base plate. Namely, it is another problem that the copper base plate can not bear the weight of the refractories and the molten metal pool over them.